I would agree with other reviewers that at the end of the cases nothing is really resolved or 'proof' given. However, there are some incidents and details of other incidents that I have never heard about - and I look into these matters fairly regularly. I have done added research on those incidents - they really happened. The people interviewed are interesting and it is good that most of their identities are revealed. There are also interviews from well-known witnesses and researchers which are quite good. This series gives a lot for us to think about.
Now, the not-so-good (or even comical element). I know that we are living in the 21st century and even documentaries have to keep with the times. There is a lot of 're-hashing' in the sequences. I think the typical viewer will be intelligent enough not to have the incident reviewed every three minutes. In addition, I am not sure why Bill (one of the History Channel investigators) is even there at all. He serves no real purpose, except to wear a baseball cap that billboards "UFO MAGAZINE" in most scenes. For those of you who haven't seen this series, imagine Johnny Carson's sidekick, Ed McMahon, as being a part of this investigation/series - well, that's Bill. He has this unnerving habit of repeating others or saying something that others have said that and somehow making it sound likes that's his original idea. He also has specific scenes that come out of nowhere and asks questions like, 'Was there a UFO here?' (duh). Bill also wears his sunglasses the majority of the time which I thought was stupid (even when working inside the studio and watching experiments), then I saw a clip when he did not wear the sunglasses. Now, I prefer him wearing the sunglasses as he has a terrible nervous squint. Anyway, if you could cut out 80% of the scenes with Bill in it the viewer would still be able to follow the case very easily and would probably be able to squeeze in 1 or 2 more DVDs in the set. (I'm sure Bill is a nice guy, but he shouldn't be on TV unless directly interviewed about something he has an original thought about).
Don't let this put you off buying this series. I gave it 3 stars, but if Bill was taken out it would have been an easy solid 4. It's really good otherwise.